Abstract: Objective:To investigate the effects and mechanism of low-frequency ultrasound in reversing multidrug re -sistance (MDR) in the MCF- 7/DOX cell line. Methods: MTT assay was used to detect the cytotoxic effect of low-frequency ultrasound and the sensitivity to Adriamycin of the MCF-7/DOX cell line. The apoptosis and concentration of Adriamycin in the cells were detected by flow cytometry (FCM). Results: Low-frequency ultrasound had a definite cytotoxic effect on MCF-7 and MCF- 7/DOX cells. The non-cytotoxic time of low-frequency ultrasound was 10 seconds. The non-cytotoxic low-frequency ultrasound significantly increased the inhibitory rate and decreased the half-maximal inhibitory concentration (IC50) value of Adriamycin in the MCF-7/DOX cell line. The IC 50 was significantly reduced from 61.08± 0.27μ g/mL to 28.12±5.94μ g/mL. The non-cytotoxic low-frequency ul trasound could partly reverse MDR in MCF 7/DOX cells by 2.17-fold in-crease. FCM suggested that low-frequency ultrasound combined with DOX could significantly increase the intracellular con centration of Adriamycin and the apoptosis of MCF- 7/DOX. Conclusion:Low-frequency ultrasound can enhance the cytotox -icity of DOX and partially reverse the DOX resistance of MCF- 7/DOX. The mechanism may be related to an increase in the permeability of the cell membrane and the concentration of intracellular DOX and may promote the apoptosis of MCF- 7/ DOX.